Method of preparing carbonaceous non-woven fabric

ABSTRACT

A METHOD OF PREPARING A CARBONACEOUS NON-WOVEN FABRIC COMPRISING BINDING CARBONACEOUS FIBERS USING AS A BINDER A HIGH MOLECULAR WEIGHT MATERIAL WHICH DOES NOT PASS THROUGH A PITCH-LIKE MOLTEN STATE DURING CARBONIZING AND THEN CARBONIZING THE SYSTEM. THE BINDER MATERIALS INCLUDE POLYMERS OF VINYLIDENE CHLORIDE, VINYLIDENE FLUORIDE, VINYL CHLORIDE, ACRYLONITRILE AND COPOLYMERS THEREOF, POLYVINYL ALCOHOL, PHENOL RESIN, EPOXY RESIN, UNSATURATED POLYESTER RESIN, FURAN RESIN AND POLYDIVINYL BENZENE RESIN.

United States Patent 'O 3,682,595 METHOD OF PREPARING CARBONACEOUSNON-WOVEN FABRIC Kensuke Okuda, 8, Ichigayadai-machi, Slunjuku-ku;Tadaaki Yoshida, 10-13, 3-chome, Nerima, Nerima-ku; and KastuyukiSugawara, 13-7, l-chome, Higaslnyulngaya Ota-ku, all of Tokyo, Japan NoDrawing. Filed May 28, 1970, Ser. No. 41,545

Claims priority, application Japan, May 28, 1969, 44/ 40,879 Int. Cl.C01b 31/02, 31/07 US. Cl. 423-447 6 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention relates to a non-woven fabric composed of almost onlycarbonaceous material prepared by binding carbonaceous fibers with abinder and then burning them.

More particularly, the present invention relates to unwoven fabricscomposed almost entirely of carbonaceous material prepared by bindingso-called carbonaceous fibers, such as blackened fibers, carbon fibers,or graphite fibers, having a length of longer than 1 mm, with a binderin a desired amount; although the method of forming a web of fibers maybe varied according to the length of the fibers and the thickness of theunwoven fabrics of this invention, and then burning them in anatmosphere which can be obtained industrially.

(2) Description of the prior art In general, carbonaceous fibers areprepared by carbonizing fibers such as rayon fibers or acrylonitrilefibers by burning them at a proper temperature, and hence in the case ofpreparing fabricated articles of carbonaceous fibers, such as spinningyarns, fabrics, and non-Woven fabrics, it is necessary to fabricate theraw fibers, such as rayon fibers r polyacrylonitrile fibers, into afabricated article and then carbonize the article. However, in such asconventional method, the efficiency of carbonization is very low(20-40%) and the weight loss and the change in diameter of the fibersare remarkable. Therefore, even if a binder is used for making suchfabricated carbonaceous articles, the binding power of the binder islost during the carbonization and the preparation of carbonaceousnon-woven fabrics having a sufl'icient strength is impossible.

The present inventors have investigated methods of making non-wovencarbonaceous fabrics by directly fabricating carbonaceous fibers withoutbeing accompanied with the aforesaid drawbacks but encountered variousdifiiculties since the materials to be fabricated are carbonaceousfibers.

That is, since carbonaceous fibers are high in rigidity and hencereadily broken, it is diificult to form a Web of such carbonaceousfibers. When the web of carbonaceous fibers is formed by a dry method ora wet method, the fundamental point is in the manner of opening the "icefibers and this difliculty has been overcome by providing a novel fiberopening method using a high speed gas stream fiber opening cylinder(Japanese patent application No. 2933/69).

Furthermore, in order to make non-woven fabrics, it is necessary tofirst fabricate the carbonaceous fibers (opened by the aforesaid manner)into a web having the desired thickness and a suitable shape, by eithera dry or wet method, and after binding them with a binder, to carbonizethe binder.

In the case of binding carbonaceous fibers with a binder by an immersionmethod, a method may be employed in which the binder is dissolved ordispersed in an aqueous dispersion of slurry of the carbonaceous fibersto bind the fibers with the binder. The carbonization following thebinding procedure is generally conducted by heattreating the fibersbound by the binder at a high temperature in an inert gas but in thiscase it is desirable to conduct the heat treatment at a temperature aslow as possible and in an industrially profitable atmosphere, forexample, for a short period of time in air.

Requirements for a binder used to prepare carbonaceous non-woven fabricsare that the binder have a definite extent of affinity to thecarbonaceous fibers when the binder is in a solid, molten or solutionstate; that the binder have a sufficient action as a carbonaceousbinder, as well as that it have a definite binding strength after it iscarbonized or during the carbonization of it. Furthermore, in the caseof easily carbonizing the binder at a comparatively low temperature,there are two kinds of binders, that is, a binder which is carbonizedthrough a state of pitch having a comparatively low viscosity and abinder which is directly carbonized without passing through such apitch-like state, it is ditficult to sufliciently bind the carbonaceousfibers and maintain the shape of the bound fibers, which makes itdifiicult to obtain sufficfiient dimensional strength of the finalproduct. Therefore, a binder which is carbonized without passing througha pitch-state is more preferable with respect to car-bonaceous fibers.

Also, the nature of carbonaceous fibers depends upon the conditions usedto prepare them; for example, they begin to have a reduction in weightor denaturation by oxidation in air, and hence a binder which can becompletely carbonized in air at a comparatively low temperature of 400to 500 C. is used with a more economical effect. Of course, if agraphitization is required, the binder may be heat-treated at asufiiciently high temperature.

SUMMARY OF THE INVENTION As the result of detailed experiments, thepresent inventors have discovered that a polymer of vinylidene chloride,vinylidene fluoride, vinyl chloride or acrylonitrile or copolymersthereof; a thermoplastic resin such as polyvinyl alcohol or a derivativethereof; or a heat-curing resin such as a phenol resin, an epoxy resin,an unsaturated polyester resin, a furan resin, and a polydivinyl benzeneresin satisfy the aforesaid conditions as a binder for carbonaceousfibers. The present inventors have succeeded in producing carbonaceousnon-woven fabrics by impregnating the carbonaceous fibers with such abinder by an immersion method or a spraying method using the aforesaidhigh molecular weight materials as the binder, either as a solutionthereof having a suitable concentration or as a latex thereof, andthereafter carbonizing the system in such a manner that the bindermaintains a sufficient binding power during the carbonization process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The concentration ofthe binder in the solution or latex may vary from 1 to 50 weightpercent.

The amount of binder impregnated into the carbonaceous fibers is below-10 weight-percent,-based on the weight of the fibers.

Any suitable solvent may be employed to dissolve the binder intosolution or to form a latex therewith. The only requirement for thesolvent is that it be compatible with the binder.

The binder-fiber system is carbonized by heating the system from atemperature of room temperature (ca. 20 C.)--200 C. to 3501000 C. at arate of about 0.5- C. per minute.

The carbonization process is carried out in air, nitrogen, argon orhydrogen, or a like atmosphere.

The molecular weight of the binder is not critical to an understandingof the present invention, as long as the molecular weight is such thatthe binder satisfy the abovedescribed requirements.

The carbonaceous non-woven fabrics thus prepared can be used not only asa heat insulating material, packing materials, and filters but also aselectric heating elements, electrodes and coating materials forantistatic purposes utilizing their conductive property.

The present invention will be further illustrated by the followingon-limiting examples.

EXAMPLE I A bundle of about 10,000 carbonaceous fibers each having adiameter of 8 microns and a length of about 7 cm. was opened into fibersby an opening method using the aforesaid high-speed gas stream fiberopening cylinder and thereafter the fibers were fabricated into a randomweb having a weight of about 200 g./cm. by means of a cyclone system.The web was immersed in a 4% solution of a binder (polyvinylidenefluoride) in dimethyl acetone to impregnate the fiber web to aproportion of about 3% by weight of binder and then the thus-impregnatedweb was burned at a temperature of 550 C. in anitrogen atmosphere. Bythe above procedure, a quite excellent carbonaceous fabric was obtained.It was confirmed by chemical analysis that about 99% of the binder wascarbonized.

EXAMPLE II A bundle of carbonaceous fibers as in Example I was cut intoa length of about 3 cm. and after being opened by the same procedure asin Example I, the fibers were fabricated into a web having weight ofabout 50 g./cm. by means of a condenser-cylinder system. A copolymer ofvinylidene chloride and vinyl chloride (70/30 Weight ratio) wasdissolved in tetrahydrofuran in a proportion of 2%. The thus-preparedsolution was applied to the web by a spraying method so that theresulting proportion of copolymer applied to the Web was about 4% basedon the weight of the web, and then the web containing the binder washeat-treated at a temperature of about 700 C. in a nitrogen atmosphereto carbonize the binder, whereby a carbonaceous non-woven fabric, inwhich the binder had almost completely been carbonized, was obtained.

EXAMPLE III A bundle of carbonaceous fibers each having a diameter of 7microns was cut into a length of about 3 mm. and was opened by means ofthe fiber opening machine as used in Example'I and the fibers were thenfabricated into a non-woven fabric by a so-called wet method using anaqueous latex dispersion of about 10% by weight of a copolymer ofvinylidene chloride and vinyl chloride 20 weight ratio). The product wasa paper-like non-woven material having a high uniformity and a weight ofabout 10 g./cm. By heat-treating the non-woven fabric at a temperature0f380 C. in air, a carbonaceous non-woven fabric having a highuniformity and a high density was obtained.

What is claimed is: I

1. A method of preparing a carbonaceous non-woven fabric which comprisesbinding a .web of carbonaceous fibers with less than 10 weight percent,based on the weight of said fibers, of a high molecular weight materialwhich does not pass through a pitch-like molten state during carbonizingselected from the group consisting of polyvinylidene fluoride andcopolymers of vinylidene chloride and vinyl chloride, and thereaftercarbonizing the binder by heating to a temperature of from 350 C. to1000 C.

2. The method of claim 1, wherein said high molecular weight material isa copolymer of vinylidene chloride and 3. The method of claim 1, whereinsaid high molecular weight material is a copolymer of vinylidenechloride and vinyl chloride.

4. The method of claim 2, wherein said binder is carbonized by heatingto a temperature of from 350 to 1000 C. at a rate of from 0.5 to 5 C.per minute.

5. The method of claim 3, wherein said binder is carbonized by heatingto a temperature of from 350 to 1000 C. at a rate of from 0.5 to 5 C.per minute.

6. The method of claim 1 wherein said binder material is applied as a 1to 50 weight percent solution or latex.

References Cited oTHER REFERENCES Kirk-Othmer' Encyclopedia of ChemicalTechnology, 2nd ed., vol. 9, 1966, pp. 840-845.

Okuda JpPolymer Science, Part A, vol. 2, 1964, pp. 17491750.

EDWARD J. MEROS, Examiner.

. US. Cl. X.R. 117-46; 204 29 V

